1. Field of the Invention
This invention relates to a method for forming container closures. More particularly, this invention relates to a method for injection molding threaded tamper indicating closures.
2. State of the Art
Many threaded closures, including tamper indicating closures having a threaded cap and a tamper, indicating band joined to the bottom of the cap by a frangible connection, are molded with a rounded thread so that the molding core can be stripped from the molded cap by axial movement, jumping the thread forming portion of the core over the internal cap thread.
Where a precision thread has been required having a sharply defined thread apex, axially split cores have been used mandating closure design where the cap skirt of the closure is at least twice as long as a cap having jump threads in order to accommodate unthreading splines or axially extending teeth. This can be seen in FIG. 1 of the closure described in U.S. Pat. No. 4,572,387 where the threaded cap 12 of closure 10 has a first skirt portion 18 having a precise internal thread 20 and a second skirt portion 24 having unscrewing teeth or spline receiving grooves 30. A splined portion of the core remains stationary, to be engaged with teeth 30, to prevent rotation of the closure as a second separate portion of the core forming the internal threads 20 is rotated in an unthreading direction.